An optical fiber may be characterized by a sensor that injects optical pulses into the optical fiber. Based on the injected optical pulses, the sensor may extract light that is scattered or reflected back from points along the optical fiber. The scattered or reflected light that is gathered back may be used to characterize the optical fiber. For example, the scattered or reflected light that is gathered back may be used to detect, locate, and measure events at any location of the optical fiber. The events may include faults at any location of the optical fiber. Other types of features that may be measured by the sensor include attenuation uniformity and attenuation rate, segment length, and location and insertion loss of connectors, splices, or any other optical components such as splitters or multiplexers.